The present invention relates to phased antenna arrays and more particularly to multi-lobe antennas particularly for base stations in communication networks.
Base station antennas generally consist of a vertically oriented linear array of antenna elements for achieving a narrow beam in elevation and a wide lobe in azimuth, providing a sufficient gain and coverage of the cell. The operator is usually demanding as small antenna units as possible due to environmental restrictions. In the perspective of the operator it is also advantageous to reduce the number of antenna units needed at a site, for example by including two or more frequency bands in one unit, i.e. co-siting, or by including more than one beam in the antenna unit. Another demand would be a base-station antenna aperture providing two beams pointing in different directions.
Prior art utilizes different approaches to solve the problem, for instance using aperture-coupled micro-strip antennas, antenna arrays and hybrid junctions.
For instance U.S. Pat. No. 5,686,926 discloses a multi-beam antenna device. Two beams with equiangular spacing are formed at a single antenna face. Multiple beams are generated by combining a plurality of such faces. The solution makes it possible to reduce the size of an antenna device and to decrease the wind load sustained by the antenna, whereby it becomes possible to mount many antennas onto a single supporting structure and to achieve substantial weight reduction of a supporting structure. However, it is apparent that a multi-beam antenna consisting of a two-element array, i.e. two vertical columns of antenna elements, where each antenna element or column is connected to a hybrid junction will not provide sufficiently good performance suitable for base station applications. A two-element array may provide the desired xc2x130xc2x0 pointing directions and a 3 dB beam-width of about 60xc2x0, but will not give sufficiently good side-lobe suppression. Simulated azimuth antenna diagrams for a two-element array at a frequency of 2045 MHz are shown in FIG. 2. The geometry of the two-element array is shown in FIG. 3. The first side-lobe of the right and left beams has its peak well above xe2x88x9215 dB and a substantial part of the power will therefore radiate into adjacent cells.
Still there is a demand for an antenna arrangement providing a compact multiple beam antenna device offering low side-lobe levels and using a reduced number of necessary panels for a base station facility with the full desired area coverage.
An antenna arrangement and an antenna system are disclosed. The inventive antenna provides an aperture generating a multi-beam pattern producing lower side-lobe levels for a base station in a communications network compared to the state of the art. The arrangement and system consist of a plurality of radiators arranged in three vertical columns of radiating elements along an antenna panel forming an aperture. A number of such panels together will form a base station antenna, where each such aperture produces two beams. Each group of three columns is further divided into sub-units for providing different elevation coverage, and each sub-unit of three separate columns is then connected to a separate beam-forming network having three output terminals forming antenna ports and two input terminals. In an orthogonal embodiment the beam-forming network generally creates a 90xc2x0 phase-gradient between the signals appearing at the antenna ports. The three radiator columns are vertically polarized and consist of the order of 2 to 8 sub-units in the elevation direction and each of the three columns contains at least three aperture-coupled radiator elements. These aperture-coupled radiator elements generally consist of patch antenna elements for instance separately fed by a strip-line network. The beam-forming networks may either be supporting a 90xc2x0 phase-gradient angle or may be supporting arbitrary angles.